Intermediate compounds of significant industrial importance are prepared by the dehalogenation of saturated halocarbons. For example, polytrifluorochloroethylene is prepared by the polymerization of trifluorotrichloroethylene, an intermediate which is prepared by the dechlorination of trifluorotrichloroethane.
In a well known process, chlorotrifluoroethane (CTFE-1113) is produced by reacting a halogenated starting material, specifically, trichlorotrifluoroethane (CFC-113), with a metallic dehalogenation agent, such as zinc dust. (In this particular reaction, zinc chloride is produced as a co-product of the reaction). The zinc dust is dissolved/suspended in a solvent, such as methanol, which acts as a carrier for the zinc. Specifically, methanol is charged to an agitated vessel and then zinc dust is transferred to the methanol-containing vessel to create a slurry. This zinc/methanol slurry is then charged as a batch to an agitated reaction vessel in which CFC-113 is fed continuously in slight excess, thereby producing a vapor product stream.
The product stream consists mainly of CTFE-1113 and its major impurities 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a), trifluoroethene (HFC-1123), 1-chloro-2,2,2-trifluoroethane (CFC-133a), and unreacted CFC-113 and methanol. The CFC-113 and methanol are removed by distillation and recycled to the reactor. The remaining impurities are removed by multiple distillation steps and finally by sulfuric acid absorption and molecular sieve adsorption to reach the final product. The organic materials remaining in the reactor after the appropriate amount of CFC-113 has been fed to the zinc batch are flashed off and recovered for yield recovery. The remaining spent batch containing zinc chloride, methanol and unreacted zinc is discharged into a vessel for further processing. Specifically, the zinc chloride and methanol are processed in multiple distillation and vaporization steps after which the zinc chloride is pumped to final product storage and the methanol is recycled for use in future batches.
The unreacted zinc remains behind in the vessel and must be periodically removed as a solid waste stream. Typically, as much as 20% of the zinc may go unreacted in the process accounting for yield losses and significant costs to remove and dispose of the waste stream. Therefore, there is a need to reduce the amount of unreacted zinc and impurities such as HFC-1123. The present invention fulfills this need among others.